Pedal Disc Research Articles

Effects of biogenic amines on the regeneration of small pieces of the pedal disc of the sea anemone Metridium senile (linnaeus)

1. The effects of the biogenic amines adrenalin and 5-hydroxytryptamine and of their respective precursors DOPA and 5-hydroxytryptophan on the regeneration of small pieces of the pedal disc of the sea anemore Metridium sinile are analysed. 2. The biogenic amines with a phenolic nucleus had a promotive effect while any eventual promotive effect of the indole alkylamines was disturbed by their toxicity. 3. These results and conclusions are compared with those obtained from similar works on animals from other invertebrate Phyla.

Delayed initiation of SS1 pulses in the sea anemone Calliactis parasitica: evidence for a fourth conducting system.

1. Single electrical shocks to the column sometimes elicit a series of 1-6 pulses in the SS1 (ectodermal slow system) but the first pulse does not appear until 5-28 s after stimulation. These pulses occur in addition to the early SS1 pulse which follows every shock and which has a conduction delay of less than 1 s. 2. The threshold of the delayed SS1 response is different from the thresholds of the three known conducting systems (through-conducting nerve net, SS1, and SS2). 3. In the case of stimulation of the column, the delayed SS1 pulses do not arise at the point of stimulation but probably originate in the tentacles or upper column. The pulse origin can shift during a single burst. 4. The pathway from the point of stimulation to the site of origin of delayed SS1 pulses is endodermal. We propose that this pathway represents a fourth conducting system (Delayed Initiation System--DIS). The DIS must connect, across the mesogloea, with the ectodermal SS1. The long pulse delay and repetitive firing may derive from pacemaker activity in the DIS. The DIS pacemakers closely resemble the pacemakers connected to the through-conducting nerve net. The DIS may be neuronal. 5. Delayed SS1 pulse bursts from unattached anemones showed an earlier onset, and more pulses/burst, than those from attached anemones. 6. Delayed SS1 pulses can also be evoked by electrical, and in some cases mechanical, stimulation of the pedal disc, tentacles, and pharynx, but there are regional differences in the number of pulses evoked, in their delay, and in their site of origin.

Dynamics of external brooding in the sea anemone Epictis Epiactis prolifera

The sexually produced young of the externally brooding actinian Epiactis prolifera Verrill, 1869 are attached to the parent's column just above the base. A transitory “brood groove” may be formed around the limbus when the parent contracts. In the population studied on the coast of Sonoma County, California, USA, from 27 to 49% of the adult anemones were brooding at any time, the proportion being inversely related to seawater temperature and directly related to size of the anemones. A brood usually consisted of young of various sizes. Overall, number of young being brooded was directly related to parent size and inversely related to size of the brooded juveniles. The growth rate of juvenile anemones was inferred to average about a millimeter in pedal disc diameter per month. Juveniles dislodged from the parent when smaller than 4 mm in basal diameter apparently cannot survive in the intertidal zone. Juveniles which successfully make the transition to adulthood have, therefore, been brooded for at least 3 months. Fewer than 50% of the smallest juveniles survived to a size at which they could live independently. The transition to adulthood was accompanied by a mortality of 80%. The survival rate, from egg to adult, was calculated to be about 1% per season.

Control of shell settling in the swimming sea anemone Stomphia coccinea.

1. Electrical activity has been recorded from Stomphia coccinea during the behavioural sequence in which the detached anemone settles on to a Modiolus shell. 2. When a responsive tentacle contacts the shell, a short, complex burst of pulses is elicited. These remain confined to the region of contact. The endodermal slow-conduction system (SS2) then begins to fire repetitively (a typical example is 16 SS2 pulses at a mean interpulse interval of 5 s) until the pedal disc begins to inflate. Shell-tentacle contact is essential for stimulation of SS2 activity. 3. The complete response, apart from local bending of the column, may be reproduced by electrical stimulation of the SS2 alone. As few as 10 stimuli at frequencies between 1 shock/s and 1 shock/10 s are required to elicit the response.

The behavior of actinians in symbiotic associations with pagurids in Japan

Behavior patterns were studied in four actinian species symbiotic with six species of Japanese pagurids. None of these actinians transferred to shells from other surfaces. Unattached Calliactis polypus clung to and settled actively on shells, whether empty or occupied by pagurids or living gastropods. After C. polypus were removed from shells, the formerly settled areas lost temporarily the capacity to elicit the settling response. Detached Paracalliactis japonica remained closed and unresponsive to shells, but when picked up by a pagurid, they relaxed and responded to shells, settling on them by blowing out an adhesive blister from the pedal disk. An unnamed actinian found only on the claw of Diogenes edwardsi responded to shells when detached but when already settled elsewhere it responded only to contact with its pagurid, detaching and settling quickly on the unoccupied chela. Unattached specimens of an unnamed species of the family Sagartiomorphidae clung to shells and settled by everting the pedal disk to form an adhesive umbrella. The discussion comments on (1) the contrast with some other symbiotic actinians which transfer to shells; and (2) the diverse ways by which actinians of different families climb on shells, suggesting that this behavior pattern evolved a number of times independently.

An electrophysiological analysis of chemoreception in the sea anemone Tealia felina

1. Electrophysiological techniques have been employed to examine the nature of the response observed in the ectodermal slow-conduction system (SSI) when dissolved food substances contact the column of Tealia felina. The response seems to consist entirely of sensory activity which may continue for periods of many minutes, provided that the stimulatory chemicals remain contacting the column. 2. The interval between each evoked pulse gradually increases as the sensory response progresses. This does not result from fatigue in the conduction system but involves a genuine process of sensory adaptation. This may occur over a period of several minutes, which is much longer than comparable adaptation in higher animals. 3. Physiological evidence suggests that the chemoreceptors involved are dispersed throughout the column ectoderm and are absent from the pedal disc, oral disc, tentacles and pharynx. 4. The basic role of the SSI in coordinating behavioural activity in sea anemones is reviewed. It is concluded that it functions primarily as a single, diffuse-conducting unit responsible for transmitting frequency-coded sensory information from ectodermal chemoreceptors to ectodermal (and perhaps endodermal) effectors.

The nature of the adhesion to shells of the symbiotic sea anemone calliactis tricolor (Leseur)

The mechanism of tentacular adhesion to gastropod shells has been demonstrated for a symbiotic sea anemone, Calliactis tricolor (Leseur) by means of scanning electron microscopy. Both basitrichous isorhiza nematocysts and spirocysts are involved with the former being much more abundant on the shells. Contrary to its classical characterization, the thread of the basitrichous isorhiza nematocyst possesses, in addition to the large spines at its base, minute spines along its length. C. tricolor whose pedal discs were attached to gastropod shells showed no difference in the number of nematocysts discharged than did those anemones whose pedal discs were attached to glass.

BURROWING BEHAVIOR OF THE SEA ANEMONEPHYLLACTIS

1. The burrowing behavior of the anemone Phyllactis is a very consistent and predictable activity.2. Burrowing is accomplished by rhythmic contractions of the column musculature around a hydrostatic skeleton, with the result that fluid is alternately forced into and withdrawn from an inflatable pedal disc. This rhythmic activity forces the disc into the sand.3. The interval between contractions is approximately 4 minutes at 21° C A pacemaker or set of pacemakers is postulated.4. Under unusual conditions rhythmic movements may continue for hours. Normally, however, the anemone stops digging within 2 hours. After the pedal disc reaches a hard substratum and sand surrounds the column rhythmic activity ceases.

The commensal association of Calliactis polypus and the hermit crab Dardanus gemmatus in Hawaii

Calliactis polypus (Forskål) lives as a commensal with various pagurids in the Pacific and Indian Oceans. In trials with the Hawaiian species, Dardanus gemmatus, the anemone, unlike the European C. parasitica, displayed only slight activity towards crabs or molluscan shells. As reported previously, crabs display a highly active behavior pattern towards C. polypus, tapping and scratching the column and eventually transferring it to its shell. The mechanical stimuli applied by the crab cause C. polypus to relax so completely that it can be lifted easily off the surface to which it was attached. Unlike C. parasitica and C. tricolor under similar circumstances, C. polypus does not release its pedal disc unaided. The tentacles and pedal disc of the detached C. polypus are extremely sticky and adhere at once to any solid surface presented to them. This enables an anemone detached by a crab to settle quickly on the shell even when only a small area of the pedal disc or only a few tentacles come into contact with the shell when placed there by the crab. The discussion emphasizes these differences in the behavior of closely related species in achieving the same ends. It also stresses that C. polypus, possessing a relatively simple nervous system, displays an impressive repertoire of responses to specific stimuli in its association with its pagurid host.

Anthopleura stellula (Actiniaria, Actiniidae) and its reproduction by transverse fission

Anthopleura stellulaEhrenberg 1834, a sea anemone from Eilat, Red Sea, is redescribed in detail and shown to be synonymous with Anthopleura elatensisEngland 1969. Asexual reproduction by autonomous transverse fission has been observed over a period of 8 months in A. stellula maintained in Mediterranean seawater (37.0 to 37.5‰ S). Fission always occurs at the same level, below the pharynx, and is followed by an asynchronous regenerative process beginning at the initial point of cleavage. The distal portion of a bisected anemone regenerates a new pedal disc, while pharyngeal formation is induced by the mesenteries of the first-budding directive tentacle in the proximal half; the original oral disc pattern is restored. After regeneration has been completed, the newly formed anemone can similarly engage in transverse fission. The fission process spreads infectionsly. If Bunodactis verrucosa, a Mediterranean anemone, is maintained in the same aquarium with A. stellula then the beginnings of fission followed by dedifferentiation are observed in the Mediterranean species, which does not ordinarily reproduce asexually. A. stellula still exhibits its induced ability to divide transversly if transferred into fresh Mediterranean seawater. When these specimens are exposed to low temperatures (12° to 13°C) for 2 months, fission activity still remains, but for only one division; there is no further fission, and no regeneration of a pedal disc. Abrupt increases in salinity to the salinity level of the Red Sea (40.0 to 41.0‰) interrupt the fission activity and pedal disc regeneration. A. stellula incised at the level where fission usually occurs promptly undergo transverse fission if cultured with other dividing anemones. However, the other anemones merely exhibit wound healing if the salinity is high. It is thought that fission and regeneration are induced by stimulating substances produced by the anemones during low salinity conditions and that the stimulating substances accumulate in the aquarium water.

The detachment of the commensal sea anemones, Calliactis polypus and C. tricolor by mechanical and electrical stimulation

1.Calliactis polypus in Hawaii and C. tricolor in Puerto Rico both respond to mechanical stimuli that resemble the activities of their commensal pagurids, e.g., stroking, tapping, scratching and squeezing of the column, by opening up, relaxing and loosening their pedal discs (Figs. 3–6).

Co-Ordination of Pedal-Disk Detachment in the Sea Anemone Calliactis Parasitica

ABSTRACT Electrical activity has been recorded from the sphincter region of Calliactis parasitica during the behavioural sequence in which the anemone detaches from the substrate and attaches to a Buccinum shell. The ectodermal slow-conduction system (SS1) fires repetitively, the majority of observed pulses occurring in the period prior to detachment (a typical example is 25 SS1 pulses at an average frequency of 1 pulse/ 7 sec.). Shell-tentacle contact is essential for stimulation of SS1 activity. Mechanical stimulation of the column excites the SS1, and 30 stimuli at a frequency of about one shock/5 sec. give pedal disk detachment. Electrical stimulation of the ectoderm excites the SS1 and about 30 stimuli at frequencies between one shock/3 sec. and one shock/9 sec. produce detachment. Detachment and the SS1 have an identical stimulus threshold. It is concluded that detachment is co-ordinated by the SS1.

The sea anemone Calliactis tricolor and its association with the Hermit crab Dardanus venosus

The association of certain sea anemones and hermit crabs is established in different ways according to the species involved. The present study shows that the behaviour patterns of the two partners in associations between Calliactis tricolor (Lesueur) and Dardanus venosus (H. M. Edwards) in the Caribbean are similar to those seen in the Mediterranean C. parasitica and D. arrosor.Although about half the crabs display an active behaviour pattern in laboratory trials, the anemone frequently settles on shells unaided and most C. tricolor respond to molluscan shells by clinging with their tentacles until the pedal disc can be attached. As a rule it is necessary for the anemone to relax and to cling to the shell if the crab is to be successful in transferring the anemone to its shell.The behaviour patterns of D. venosus include a distinctive tapping of the edge of the base of C. tricolor after which the anemone is pulled or lifted off and transferred to the shell. An experimenter can also cause the anemone to relax and to detach itself by tapping the edge of the base with plastic rods after the manner of the crab.The mechanisms by which the tentacles of Calliactis cling to, and by which the base settles upon, shells still remain to be elucidated. The participation of nematocysts in these processes could not be demonstrated in this study. C. tricolor is found on some other pagurid and non‐pagurid crabs in various localities. These associations need to be investigated fully in order that the behaviour patterns of C. tricolor may be correctly interpreted and compared with those of other species of Calliactis.

The pedal disc of the swimming sea anemone Stomphia coccinea during detachment, swimming, and resettlement

The pedal disc was studied during the "swimming" response of Stomphia coccinea by use of photography and visual aids, certain experimental procedures, and histological preparations. At the moment of release, deep ridges and clefts appeared along the lines of the mesenteries, reducing the surface area by about one-half. Circular muscles on the pedal disc and vertically inserted muscles at the bases of the mesenteries were seen. These together would account for the observed pattern. The breaking of the adhesive sole by the furrowing of the surface, the concavity of the pedal disc produced by parietobasilar contractions, and the dissolution of an adhesive substance seemed all to be involved in the detachment of the animal in response to a swimming stimulus. During the resettling of S. coccinea after swimming, the pedal disc became very sticky, especially if the tentacles had touched the shell. This stickiness coincided with a general discharge of nematocysts (microbasic p-mastigophores) from the pedal disc. The active functions of the pedal disc in the release and resettlement of S. coccinea were discussed and it was pointed out that the basal area is by no means a passive element in the behavior patterns of actinians.

THE RESPONSE TO MOLLUSCAN SHELLS OF THE SWIMMING SEA ANEMONES STOMPHIA COCCINEA AND ACTINOSTOLA NEW SPECIES

Behavior patterns in the sea anemones Stomphia coccinea and Actinostala new species are described by which these animals settled preferentially on shells of Modiolus modiolus (commensal of S. coccinea) after they have been made to swim in response to the appropriate stimuli (the starfishes Dermasterias or Hippasteria, the nudibranch Aeolidia papillosa, etc.). Tentacular and oral contact without adhesion, followed by great distension of the pedal disc and some flexion of the column towards the shell, were the main components of these behavior patterns. Anemones which had been allowed to settle on other surfaces not more than 6 h previously migrated to shells which were brought into contact with the tentacles. Shells which were boiled in alkali to remove organic matter lost their capacity to elicit the response. This behavior pattern is compared with that of Calliactis parasitica, a commensal of hermit crabs which shows a preference for settling on shells of large gastropods.

SOME ASPECTS OF THE STRUCTURE OF THE NERVOUS SYSTEM IN THE ANEMONE CALLIACTIS.

In the light of existing work on tbe behavioral physiology of this anemone, the structure of parts of the neuroimiscular system has been examined in detail. In the sphincter region, the morphological basis for rapid through-conduction and motor innervation is a network of bipolar nerve cells, which is connected to the similar retractor nerve-nets of mesenteries. Sphincter muscle fibers are arranged at the periphery of tubes, which form a meshwork within the mesogloea. Bipolar nerve cells appear to run in these tubes. Neurites also reach the sphincter from the endodermal nerve-net by penetrating the mesogloea directly. The nerve-net over the circular muscle is richer than in other parts of the column, but shows similar features. It includes small multipolar cells of unknown function. Coordination between different parts of the anemone is discussed in terms of possible pathways for the transmission of excitation. For example, bundles of retractor and parietobasilar muscle fibers continue from both surfaces of mesenteries into the mesogloea of the pedal disk, suggesting a possible route for neurites passing to or from the ectoderm. If confirmed, the existence of this route could throw light on a number of sequences of behavior.

Preferential Settling of the Sea Anemone Stomphia coccinea on the Mussel Modiolus modiolus

In resettling after its "swimming" response, Stomphia shows a special behavior pattern when in contact with bivalve shells. Movements of the tentacles, oral disc and column, and huge swellings of the pedal disc are the chief features in a coordinated purposive sequence, which settles the anemone on the shell in a few minutes.

INHIBITION OF THE SWIMMING RESPONSE BY FOOD AND OF NEMATOCYST DISCHARGE DURING SWIMMING IN THE SEA ANEMONE STOMPHIA COCCINEA.

ABSTRACT The discharge of tentacular nematocysts in response to food was studied in Stomphia coccinea before and during swimming, and during the period of resettling. The tendency of Stomphia’?, nematocysts to discharge on contact with food virtually disappeared during the swimming response. The disappearance of the nematocyst response coincided with the release of the pedal disk; its reappearance coincided with the re-attachment of the pedal disk. Objects rubbed on the aboral surface of Dermasterias can cause swimming if brought into contact with a single tentacle of Stomphia. A general inhibition of the swimming response to objects rubbed on Dermasterias was set up by flooding the tentacular crown with a food extract. A local inhibition was set up when food was applied to a single tentacle just before the same tentacle was touched with material from Dermasterias. The results are discussed in relation to the view that nematocysts function as independent effectors.

The nerve-net of a swimming anemone, Stomphia coccinea

ABSTRACT The nervous system of this anemone has been examined in an attempt to study the pacemaker system, previously thought to be localized in the median zone of the column. No clear-cut nerve-ring has been found. The whole column, however, is characterized by the presence of large multipolar nerve-cells in the endoderm, to which pacemaker activity is provisionally attributed. There are several thousand of these cells and their neurites connect with those of other nerve-cells and sense-cells in the column, and with the mesenteric nerve-nets. The column nerve-net, of which the multipolars form part, conducts slowly and fatigues easily. Present physiological evidence from Stomphia and other coelenterates does not invalidate the suggestion that the multipolar cells may also function as a pacemaker system. Other features of the nervous and sensory systems are very like those of other anemones (e.g. Calliactis, Metridium). The column, mesenteries, and oral and pedal disks are briefly described; much information is still lacking. As expected, sense-cells are aggregated along the angles of the mesenteries except in the pharynx. Their neurites connect with the column nerve-net, and with the mesenteric nerve-nets. A well-developed network of bipolar nerve-cells on the retractor surface may be regarded as a rapid through-conduction tract. As in Metridium and Calliactis the radial nerve-net on the opposite face of the mesentery is similar but much sparser. The ectodermal surface of the oral disk, as described by the Hertwigs, shows a criss- cross network of bipolar nerve-cells together with radial rows of small multipolar nerve-cells above the septa. These might perhaps have a proprioceptive function. In the endoderm of the pedal disk, sense-cells are numerous but nerve-cells few. These features are discussed only in so far as they may be related to the swimming behaviour of Stomphia.

The response of the sea anemoneCalliactis parasiticato shells of the hermit crabPagurus bernhardus

The five stages in the behaviour pattern by whichCalliactis parasiticatransfers to shells ofBuccinum, normally occupied byPagurus bernhardus, are described. The first of these, the clinging of tentacles to shell, is a trigger for the pattern as a whole; it occurs inCalliactisalready settled on glass or plastic, and more consistently, inCalliactiswhose pedal disks are unattached. Tests on the frequency and speed of the clinging response under various conditions gave this information: (a) individual shells used byPagurusvary greatly in potency; (b)Calliactiscling to shells ofPectenandMytilus, but only erratically and after long delays; (c)Buccinumshells that have never been occupied by crabs, evoke the clinging response most consistently and rapidly; (d) removal of periostracum fromBuccinumshells reduces, but does not abolish, clinging, thoughCalliactisresponds to isolated strips of periostracum as to a shell; (e)Calliactisdoes not cling to dummy shells, to shells boiled in alkali, or to shells coated with a thin plastic layer; (f)Calliactisdoes not cling to inactivated shells when these are re-occupied by crabs. It is concluded that the clinging response depends entirely on a general molluscan shell-factor. In the settlement of the foot on the shell (the fourth stage of the behaviour pattern), a specific response to shell-factor is also involved. Vertical incisions, even complete bisection, do not abolish clinging but merely slow down the orderly pattern of the transfer to a shell. Horizontal incisions impair the pattern more. Complete horizontal section, including removal of the pedal disk alone, abolishes the clinging response and the whole behaviour pattern. Interposed stimuli show features consistent with a 5-stage programme in which the com­pletion of each stage is a trigger for the next. But each stage may be greatly prolonged, and, if interrupted, starts again. The neuromuscular links required to co-ordinate this behaviour pattern are listed and discussed.